1. Field of the Invention
The present invention belongs to the technical field of ink jet recording devices comprising an ink jet head having a first nozzle for ejection of droplets of pigment ink and a second nozzle for ejection of droplets of dye ink.
2. Description of the Prior Art
Generally, pigment inks containing a pigment as a coloring agent exhibit excellent light resistance and water resistance with respect to plain paper (i.e., widely available commercial paper particularly for use by electrophotographic copying machines, which is, however, not manufactured with the intention of providing an optimum structure, composition, and characteristic suitable for ink jet recording devices) and special paper intended for use in ink jet recording (i.e., paper having an ink receiving layer on substrate). In spite of such properties, pigment inks, because of their relatively narrow color reproduction range, prove unsuitable for special paper requiring high level color reproducibility. Additionally, pigment inks, particularly color inks, exhibit extremely poor permeability, therefore proving unsuitable for permeable films (OHP sheets) either. On the other hand, dye inks containing a dye as a coloring agent, have a wider color reproduction range in comparison with pigment inks but are unsuitable for plain paper because of being poor in light resistance as well as in water resistance with respect to plain paper.
With a view to producing excellent images regardless of the type of recording paper, Japanese Unexamined Patent Gazette No. H11-1647 proposes a technique in which both dye ink and pigment ink are prepared. Whereas droplets of the dye ink are for effecting recording on special paper, recording on plain paper is effected by laying droplets of the dye and pigment inks one on top of the other.
Such proposal, however, remains open to further improvement. In other words, the foregoing arrangement of merely preparing both dye ink and pigment ink for changing ink to be ejected by the type of recording paper fails to provide any sufficient counterbalancing advantage to the increase in ink jet head cost.
Bearing in mind the above-described drawback with the prior art technique, the present invention was made by moving forward with the arrangement in which both dye ink and pigment ink are prepared. Accordingly, an object of the present invention is to produce images superior in characteristics such as water resistance and color reproducibility for any type of recording paper, and to improve cost-performance by permitting selection between a mode of high image-quality recording operation and a mode of fast recording operation.
In order to achieve the object, in the present invention, either the maximum amount of ejection of a droplet of dye ink that is ejected from a second nozzle is set lower than the maximum amount of ejection of a droplet of pigment ink that is ejected from a first nozzle, or the density of a droplet of dye ink that is ejected from a second nozzle onto recording paper is set lower than the density of a droplet of pigment ink that is ejected from a first nozzle onto recording paper.
The present invention provides a first ink jet recording device comprising an ink jet head having a first nozzle for ejection of droplets of pigment ink containing a pigment as a coloring agent and a second nozzle for ejection of droplets of dye ink containing a dye as a coloring agent so that recording is effected by ejection of ink droplets from at least either the first or second nozzle of the ink jet head onto recording paper, wherein the maximum amount of ejection of a droplet of the dye ink that is ejected from the second nozzle is set lower than the maximum amount of ejection of a droplet of the pigment ink that is ejected from the first nozzle.
In accordance with the above-described construction, for the case of the dye ink, a plurality of ink droplets whose ejection amount is set smaller are laid one on top of the other to effect recording, thereby freely producing dots of small diameter and dots of large diameter for the achievement of high image-quality recording. For the case of the pigment inks, since the amount of ejection is large, high-speed recording can be effected, although image quality drops somewhat. Generally, whereas high image-quality is required for recording on special paper, high-speed recording is required for recording on plain paper. Accordingly, such arrangement that recording on special paper is effected by dye ink droplets while on the other hand recording on plain paper is effected by pigment ink droplets will not only produce images superior in characteristics such as water resistance and color reproducibility on both types of paper but also meet the foregoing requirements. Further, if recording on a transparent film is effected by dye ink droplets, this eliminates the problem of permeability. Accordingly, it is possible to change a type of ink that is ejected and, in addition, it is possible to permit selection between a mode of high image-quality recording operation and a mode of high-speed recording operation, therefore providing improvements in cost-performance.
It is preferred that the diameter size of the second nozzle be set smaller than that of the first nozzle in the first ink jet recording device.
Because of such arrangement, the amount of ejection of dye ink droplets (the maximum ejection amount) can be further decreased, while on the other hand the amount of ejection of pigment ink droplets (the maximum ejection amount) can be further increased. In the case the first nozzle is identical in diameter size with the second nozzle, although it is possible to change ejection amounts by making pulse waveforms, which are applied to actuators operative to cause ejection of each ink droplet, different from each other, there are limits of setting a great difference in ejection amount between dye and pigment ink droplets. In the present invention, however, the diameter size of the second nozzle is set smaller than that of the first nozzle, which facilitates allowing these nozzles to eject their respective ink droplets at different ejection amounts. In addition, the difference can be expanded considerably.
Preferably, the first nozzle is formed in a first nozzle formation member disposed on a portion of a surface of the ink jet head and the second nozzle, which is smaller in diameter size than the first nozzle, is formed in a second nozzle formation member disposed, in juxtaposition with the first nozzle formation member, on the ink jet head surface portion, in the first ink jet recording device.
As a result of such arrangement, pigment ink liable to cause clogging does not easily adhere to the surface of the second nozzle formation member, therefore controlling clogging of the second nozzle of small diameter by pigment ink.
Preferably, the first ink jet recording device is provided with a first blade for wiping off pigment ink adhered on a surface of the first nozzle formation member and a second blade for wiping off dye ink adhered on a surface of the second nozzle formation member. This arrangement definitely ensures that clogging of the second nozzle by pigment ink can be controlled.
The present invention provides a second ink jet recording device comprising an ink jet head having a first nozzle for ejection of droplets of pigment ink containing a pigment as a coloring agent and a second nozzle for ejection of droplets of dye ink containing a dye as a coloring agent so that recording is effected by ejection of ink droplets from at least either the first or second nozzle of the ink jet head onto recording paper, wherein the density of a droplet of the dye ink that is ejected from the second nozzle onto the recording paper is set lower than the density of a droplet of the pigment ink that is ejected from the first nozzle onto the recording paper.
In accordance with such arrangement, the dye ink density is set lower. A plurality of ink droplets of the dye ink are laid one on top of the other to effect recording, thereby producing in a free manner dots of low density and dots of high density for the achievement of high image-quality recording. On the other hand, although the pigment ink is able to produce only dots of high density, there is no need for laying a plurality of pigment ink droplets one on top of the other. This allows pigment inks to achieve high-speed recording. As a result, like the first ink jet recording device, such arrangement that recording on special paper is effected by dye ink droplets while on the other hand recording on plain paper is effected by pigment ink droplets will not only produce images superior in characteristics such as water resistance and color reproducibility on both types of paper but also effect high image-quality recording on special paper and high-speed recording on plain paper.
In each of the first and second ink jet recording devices, it is preferred that the ink jet head further has a first actuator for causing, when a first drive pulse is applied thereto, ejection of a droplet of the pigment ink from the first nozzle and a second actuator for causing, when a second drive pulse is applied thereto, ejection of a droplet of the dye ink from the second nozzle, and that the ink jet recording device further comprises drive signal generation means for generating a drive signal in which the first and second drive pulses repeatedly occur and drive pulse selection/application means for selecting between the first drive pulse and the second drive pulse from the drive signal generated by the drive signal generation means so that, when the first drive pulse is selected, the selection (i.e., the first drive pulse) is applied to the first actuator, while, when the second drive pulse is selected, the selection (i.e., the second drive pulse) is applied to the second actuator.
This accordingly eliminates the need for individually generating a first and a second drive pulse. Generation of a single drive signal including first and second drive pulses therefore suffices. This cuts down the cost of drive circuits for the first and second actuators.
It is preferred that the drive signal generation means is so constructed as to generate a drive signal which repeats a pulse occurrence operation in which, after a succession of occurrences of a plurality of second drive pulses, a less number of first drive pulses than the number of the successively-occurred first drive pulses occur.
Such arrangement, since recording pixel density is generally made higher when recording is effected by dye ink droplets in comparison with when recording is effected by pigment ink droplets, makes it possible to set the numbers of first and second drive pulses according to the recording pixel density difference, whereby optimum drive signals can be obtained.
When a drive signal is generated which repeats a pulse occurrence operation in which, after a succession of occurrences of a plurality of second drive pulses, a less number of first drive pulses than the number of the successively-occurred first drive pulses occur, it is preferred that the drive signal generation means is so constructed as to generate a drive signal in which a second drive pulse occurs at fixed intervals.
Because of such arrangement, when ink droplets are ejected onto recording paper while the ink jet head is moved with respect to the recording paper at an approximately fixed speed, dye ink droplets fired from the second nozzle land on the recording paper to be spaced at equal intervals, thereby coping with high image-quality.